The invention set forth in this specification pertains to new and improved expansion fasteners. More specifically the invention set forth in this specification pertains to an expansion fastener each of which is adapted to be supported within a hole in a first member in such a manner so as to be capable of being inserted into a hole in a second member and which is adapted to be manipulated when a part of it is within the hole in the second member so as to be expanded into engagement with the interior of the hole in the second member. Expansion fasteners of this category may be utilized with a wide variety of different applications. They are primarily utilized in various different locations where that it is only possible to gain access to the hole in the second member from one side or surface of the second member.
It is possible to construct expansion fasteners capable of being utilized in the manner indicated in the preceding paragraph in a number of different ways. It is considered that it has been most advantageous to construct expansion fasteners capable of being utilized as discussed in the preceding in the manner indicated in the Pitzer U.S. Pat. No. 3,373,648, issued Mar. 19, 1968 entitled "Fasteners with Expansion Sleeve". Fasteners of the type referred to in this discussion and in this patent have normally been constructed so as to utilize an externally threaded shaft provided with a head capable of being engaged with a manipulative tool so as to turn the shaft, a generally cylindrical, longitudinally split sleeve located around the shaft and a nut threaded on the shaft. In such a structure the sleeve and the nut include coacting conical surfaces serving to expand the sleeve as the nut is moved on the shaft towards the head. Because of their functions these surfaces can be referred to as expansion surfaces.
Fasteners of this type are normally constructed so that the shaft is capable of fitting through a hole in a first member but so that neither the head on the shaft nor the sleeve is capable of passing through this hole. A fastener of the type described herein is normally assembled on such a first member with the head and the sleeve on opposites sides of the first member so that both the sleeve and the nut extend outwardly around the shaft from one side of the first member. In this type of fastener normally both the nut and the unexpanded sleeve are dimensioned so as to be capable of fitting through a hole in a second member as previously indicated. Further these parts are dimensioned so that only a comparatively limited amount of rotation of the threaded shaft is necessary in order to expand the exterior of the sleeve into contact with the interior of the hole in the second member.
One of the major problems encountered with prior expansion fasteners of the type discussed in the preceding concerns the fact that dimensions of the parts with the sleeve in an unexpanded configuration should be such that there will be no relative rotation between the sleeve and the hole in the second member. When such relative rotation occurs the fastener will not expand as it is used but will rotate freely as the head of the shaft is turned. This, of course, is undesirable. In order to insure adequate friction to insure expansion it has been very important to dimension the parts so that there is a degree of contact between them sufficient to inhibit such relative rotation. This, of course, is somewhat expensive and, hence, undesirable.